 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.expressions;

 import org.eclipse.core.runtime.CoreException;

 /**
  * An evaluation context is used to manage a set of objects needed during
  * XML expression evaluation. A context has a parent context, can manage
  * a set of named variables and has a default variable. The default variable
  * is used during XML expression evaluation if no explicit variable is
  * referenced.
  * <p>
  * This interface is not intended to be implemented by clients. Clients
  * are allowed to instantiate <code>EvaluationContext</code>.
  * </p>
  *
  * @since 3.0
  */
 public interface IEvaluationContext {

     /**
      * Returns the parent context or <code>null</code> if
      * this is the root of the evaluation context hierarchy.
      *
      * @return the parent evaluation context or <code>null</code>
      */
     public IEvaluationContext getParent();
     
     /**
      * Returns the root evaluation context.
      *
      * @return the root evaluation context
      */
     public IEvaluationContext getRoot();
     
     /**
      * Specifies whether this evaluation context allows activation
      * of plug-ins for testers used in the expression tree. To actual
      * trigger the plug-in loading this flag has to be set to <code>
      * true</code> and the actual test expression must have the
      * attribute <code>forcePluginActivation</code> set to <code>
      * true</code> as well.
      *
      * @param value whether this evaluation context allows plug-in activation
      * @since 3.2
      */
     public void setAllowPluginActivation(boolean value);
     
     /**
      * Returns whether this evaluation context supports plug-in
      * activation. If not set via {@link #setAllowPluginActivation(boolean)}
      * the parent value is returned. If no parent is set <code>false</code>
      * is returned.
      *
      * @return whether plug-in activation is supported or not
      * @since 3.2
      */
     public boolean getAllowPluginActivation();
     
     /**
      * Returns the default variable.
      *
      * @return the default variable or <code>null</code> if
      * no default variable is managed.
      */
     public Object getDefaultVariable();
     
     /**
      * Adds a new named variable to this context. If a variable
      * with the name already exists the new one overrides the
      * existing one.
      *
      * @param name the variable's name
      * @param value the variable's value
      */
     public void addVariable(String name, Object value);
     
     /**
      * Removes the variable managed under the given name
      * from this evaluation context.
      *
      * @param name the variable's name
      * @return the currently stored value or <code>null</code> if
      * the variable doesn't exist
      */
     public Object removeVariable(String name);
     
     /**
      * Returns the variable managed under the given name.
      *
      * @param name the variable's name
      * @return the variable's value or <code>null</code> if the content
      * doesn't manage a variable with the given name
      */
     public Object getVariable(String name);
     
     /**
      * Resolves a variable for the given name and arguments. This
      * method can be used to dynamically resolve variable such as
      * plug-in descriptors, resources, etc. The method is used
      * by the <code>resolve</code> expression.
      *
      * @param name the variable to resolve
      * @param args an object array of arguments used to resolve the
      * variable
      * @return the variable's value or <code>null</code> if no variable
      * can be resolved for the given name and arguments
      * @exception CoreException if an errors occurs while resolving
      * the variable
      */
     public Object resolveVariable(String name, Object [] args) throws CoreException;
 }
